Well drilling method



Dec. 31, 1968 w. D. ELENBURG WELL DRILLING METHOD Sheet Filed April 6, 1967 INVENTOH.

WAYLAND D. ELENBURG 6 8% 47' TOR/V575 Dec. 31, 1968 w. D. ELENBURG WELL DRILLING METHOD Sheet Filed April 6, 1967 WAYLAND D. ELENBURG By Iva g 6? SW ATTORNEYS United States Patent 3,419,092 WELL DRILLING METHOD Wayland D. Elenburg, Wichita Falls, Tex., assignor to Walker-Neer Manufacturing, Inc., Wichita Falls, Tex., a corporation of Texas Continuation-impart of application Ser. No. 574,054, Aug. 22, 1966. This application Apr. 6, 1967, Ser. No. 628,958

Claims. (Cl. 17569) ABSTRACT OF THE DISCLOSURE A well drilling method using dual drill pipe with drilling fluid being circulated down through the annulus between the pipes and up through the inner tube, carrying cuttings and cores to the surface, Circulation is started by pumping fluid down 'bot'h passages until increase in pressure indicates penetration to a relatively non-porous formation. Gas may be pumped down the inner tube to lighten the liquid head before regular circulation is commenced. Circulation up through the hole annulus is restricted mechanically 'and/ or by introducing a heavy static fluid to balance the light circulating fluid which, since confined to the pipe, flows at a high rate. Air may be introduced into the inner pipe fluid to increase the difference in the static head of the fluid columns within the pipe.

This application is a continuation-in-part of my copending application Ser. No. 574,054 filed Aug. 22, 1966. This invention relates to a well drilling method and more particularly a well drilling method involving variations of reverse circulation of well drilling fluid.

In conventional drilling utilizing a single drill pipe, the flow of drilling fluid in one direction, the rising stream in the case of conventional circulation and the down flowing stream in the case of reverse circulation, is through the hole annulus around the drill pipe. The circulating fluid, therefore, is subjected to flow through a conduit of wholly unpredictable nature and cross-section. For eX- ample, when passing through a fissure or other lost circulation zone, all or most of the stream flowing through the hole annulus simply flows out into the fissure, and until the fracture is plugged, complete circulation is not possible. Moreover, while it is the principal purpose of conventional drilling simply to make hole, it is obviously a distinct advantage to retrieve recognizable cuttings which would identify the nature of the sub-surface formation being penetrated. However, in order to avoid fracturing sub-surface formations, it is necessary to circulate the drilling fluid at low flow rates and relatively low pressures, and it is, therefore, extremely diflicult to lift cuttings from the bottom of the bore hole before they are pulverized into unrecognizable, minute chips. Moreover, even if the cuttings could be identified at the surface, their retrieval is of little value unless it is also possible to determine the depth from which they were severed. At the low flow rate required, the arrival of the cuttings at the surface is largely affected by the weight of the chips being retrieved, and, hence, a small chip from a relatively deep formation may arrive at the surface prior to a larger chip from a shallower formation. Hence, there is no way a driller can determine with any degree of specificity the complete information required for formation identification. That is, unless both the nature of the formation and the depth at which it exists can be dedetermined, the geologists information cannot be complete. Moreover, portions of the well bore may become enlarged as by washing away or collapsing to provide traps wherein chips may become lodged for a suflicient period of time that the depth which might be presumed from their time of arrival would be far greater than that at which they were actually severed.

It is, therefore, an object of this invention to provide a method of drilling wells with dual passage drill pipe wherein recognizable cuttings may be retrieved at the surface quickly and in almost precisely the order in which they were severed.

It is a further object of this invention to provide a method of well drilling wherein the circulation of fluid is confined within the drill pipe with virtually no loss even when starting a hole or when passing through a lost circulation zone.

It is a further object of this invention to provide a method of circulation through dual passage drill pipe which further facilitates the retrieval of the cores or cuttings.

It is a further object of this invention to provide a method of circulation through dual passage drill pipe to facilitate initiation of drilling in off-shore formations.

In carrying out this invention, I-provide dual passage drill pipe with a bit capable of cutting sub-surface samples in the form of large chips or cores, together with means of fluid circulation that insures the rapid and orderly retrieval of such samples at the surface. For ordinary drilling, the fluid carrying the samples, whether it be gas or liquid, is circulated at a much higher rate than in conventional drilling, an annular protuberance being carried above the bit to greatly restrict the amount of fluid that can flow up through the hole annulus. In addition, the concentric drill pipe with restricting annular protuberances provides a wide diversification of circulating methods. For example, when drilling with liquid it may be found desirable to use a heavy and/ or viscous fluid in the hole annulus to prevent blow out and fluid loss, a viscous fluid not being nearly as vulnerable to loss in a fractured or porous formation. The viscous fluid is conveniently introduced into the hole annulus by blocking off the inner tube and pumping it down through the outer pipe annulus so that pump pressure is not asserted directly against the formation. In the same manner, the driller may introduce a gelatinous fluid into the hole to seal off the sub-surface formations and protect the wall of the hole from hydration and fluid currents. Moreover, the gelatinous fluid may augment or replace the annular protrusion above the bit by blocking flow of the lighter drilling fluid in the hole annulus.

With dual passage drill pipe, a well may be started in an ofl-shore location by pumping air or other gas down through the central annulus to evacuate it so that when normal, reverse circulation is started, with sea water, if desired, the circulating fluid will follow the path of least resistance up through the evacuated inner tube. As an additional feature, I have found it desirable at times to introduce compressed air or other gas into the downflowing stream, with ports or other orifices being provided at the drill bit or in the pipe above the bit so that a portion of the downstream is relieved into the inner tube, whereby the gas expands to make the inner fluid column lighter and increase the differential in the static head of the outer fluid column.

Other objects and advantages of this invention will become apparent from the description following when read in conjunction with the accompanying drawings,

' wherein:

FIG. 1 is a more or less schematic diagram of the drilling method of this invention utilizing dual passage drill p p FIG. 2 is a section view taken along line 2-2 of FIG. 1;

FIGS. 3 and 4 are partial section views showing initial circulation for off-shore drilling;

FIG. 5 is a partial schematic section view showing the method in greater detail; and

FIG. 6 shows another embodiment of my drilling method.

Referring now more particularly to FIG. 1, I have shown in more or less schematic form my drilling apparatus 10 comprising dual passage drill pipe 12 including outer and inner pipes 14 and 16, respectively. As shown, the pipes may be spaced and centered by suitable spacer webs 17. The two pipes 14 and 16 provide an annular outer passage 18, normally for downward circulation, and an inner circular flow passage 20. While this invention is not restricted to the use of dual passage pipe of any specific construction, it has been found desirable to use the dual passage pipe disclosed in Henderson US. Patent No. 3,208,539, granted Sept. 28, 1965. At the lower end of the drill pipe I have illustrated a rock bit 22 including a skirt or shroud 24 and conical cutting members 26, only one of which is shown for clarity of illustration. The rock bit is designed to cut sizeable chips C suitable for analysis and may be of the type shown in my aforesaid co-pending application Ser. No. 574,054, filed Aug. 22, 1966. The shroud 24 virtually confines fluid circulated down through the outer passage 18 and out the bit jet ports 27 to an upward course through the inner pipe passage 20 and not through the well annulus A.

Spaced a short distance above the bit, I provide an annular barrier 28 which, as shown in FIG. 2, is provided with a series of recesses 30 .and may include cutting edges 32 so that the barrier 28 engages the wall of the well bore W to provide a barrier against all but a limited amount of fluid flow up through the annulus A.

The dual passage drill string 12 may be rotated by any suitable means, but for purposes of illustration I have shown a large pinion 34 which is secured to a swivel 36 and driven by a small gear 38 through any suitable power source, such as a hydraulic motor 40. The power swivel 36 is raised and lowered within the rig (not shown) by any suitable means such as a bale 42. A drilling fluid conduit 44 conducts drilling fluid from any suitable source to the outer flow passage 16 and a goose neck 46 delivers cuttings from the sub-surface formation to any suitable separator 48 to separate the cuttings from the fluid. Also in communication with the inlet conduit 44 is a branch line 50 connected to a large capacity air compressor 52 so that air or other compressed gas may be employed as the drilling fluid medium or for auxiliary purposes hereinafter to be described. A valve 54 is provided so that the air compressor may be used selectively. The fluid inlet line 44 is provided with a high-velocity pump 56 and valve means 58 may be interposed in the line so that the fluid flow may be interrupted or directed selectively to the outer passage 18 and/ or to the inner passage 20 through by-pass line 44a and goose neck 46.

In FIG. 1 I have illustrated the drilling apparatus 10 in use over a body of water and, as shown, the sea Water S may be the circulating medium. However, it is to be understood that this invention is not confined to use in offshore locations, and it will become apparent that while special problems are presented in off-shore drilling there are many problems and solutions common to drilling on land once the ocean floor formations F have been penetrated.

Referring now to FIGS. 1, 3 and 4, I have illustrated a special solution afforded by the method of this invention to problems of off-shore drilling. In starting a hole from a boat, barge or off-shore platform, the drill pipe 12 is simply lowered from the off-shore platform and it will normally be disposed substantially vertically so that the hole will be started directly under the platform. Then, as drilling is commenced in the soft ocean floor F fluid is pumped down both pipe passages 18 and 20 until the bit has penetrated sufliciently that the sub-surface formation F provides some resistance to flow. If this does not occur in the ocean floor sludge F sufficient resistance to flow should occur by the time the bit shroud 24 and the annular barrier 28 penetrate the underlying firmer formations F Then, the pump 56 is shut down and the air compressor 52 activated to force air through the air by-pass line 59a and down the inner tube 16 until the inner tube is wholly or partially evacuated of drilling fluidand occupied instead by the air, as shown in FIG. 4. Then, the pump is activated and normal circulation is started with the liquid being pumped down the annular space 18 between the pipes 14 and 16. Most of the return flow will naturally follow the path of least resistance up through the evacuated inner pipe 15 inasmuch as flow up the hole annulus is opposed by the static head of the sea water 5. Of course, some small percentage of the fluid may pass up through the hole annalus A, but not enough to cause any serious loss of circulation. Moreover, with sea water being used as the circulating medium, fluid loss is not a problem in offshore drilling. In any event, after further bit penetration, the bit shroud 24 and the annular barrier 28 further protect the sub-surface formations F and F against fracturing by the pressure of the circulating fluid and, hence, the fluid may be circulated at extremely high rates for superior chip recovery.

According to another feature of this invention, the air compressor 52 may be activated simultaneously with the pump 56 so that the drilling fluid is aerated under pressure during its downward flow. Then, a series of ports 60 may be provided at various locations along the length of the inner tube 16 so that some of the aerated fluid will be diverted directly into the inner passage 20'. Upon passing through the ports 60, the fluid is released to a relatively low pressure zone within the inner tube and the air expands to form a series of bubbles B within the inner tube to lighten the hydrostatic head of the fluid within the inner tube. The resultant difference in hydrostatic head facilitates elevation of the fluid within the inner tube carrying the cuttings up through the goose neck 46. Thus, by blocking upward flow in the hole annulus past the annular barrier, an off-shore well may be started and completed to the extent determined by the life of the drill bit without casing the hole. This permits an investigation of the sub-surface formations F to the depth drilled, and extremely valuable information is retrieved without attempting to solve the diflicult problem of reentry into the hole A after changing the bit.

Referring again to FIG. 1, this process is very effective for drilling through lost circulation zones F because the bit shroud 24 and the annular barrier 28 are effective to restrict fluid from coming up the hole annulus W. Of course, while passing through the porous or fractured zone F some fluid is lost to the formation, but after drilling a very short distance deeper, sometimes two feet or less below the lost circulation zone F fluid loss to the formation is reduced to a very small percentage of that circulated down the outer pipe annulus 18. Moreover, if the barrier 28 is not adequate to retard fluid loss, compressed air can be injected into the drilling fluid as previously de scribed to form bubbles B and lighten the hydrostatic head of fluid in the inner tube 16 and decrease the fluid loss because of greatly reduced resistance to fluid flow up the inner tube.

Because the barrier greatly restricts fluid flow in the hole annulus A, the formations being drilled are protected against fracture by the pressure of the fluid. Therefore, I have found it highly desirable to circulate the fluid at a rate greatly in excess of circulation with conventional drilling. For example, when liquid is employed, I use a high capacity pump 56 and circulate the fluid at a high rate on the order of to gallons per minute. With an outer drill pipe of the diameter of 4% inches, the flow up the inner tube is at a rate of approximately 600 feet per minute and, hence, the cuttings are retrieved at an extremely rapid rate. Moreover, the large and small cuttings will ascend at approximately the same rate. Hence, not only are the cuttings retrieved within a very few minutes after being separated from the formation, they are received in proper order, resulting in much more accurate information as to the depth from which the cuttings were severed. An additional advantage in circulating fluid at a high flow rate resides in the fact that the cuttings are very quickly moved from under the bit and are, therefore, projected up the inner tube before they are completely pulverized.

Of course, this circulation at high velocity can also be accomplished by air or gas and, for this purpose, a high capacity compressor 52 may be provided to circulate at a high rate. I have found that by delivering approximately 200 cubic feet per minute of air to the outer fluid passage, the return is almost instantaneous, in excess of 5,000 feet per minute.

As previously described, in accordance with the method of this invention a hole is started by pumping fluid slowly down both the inner and outer tubes until a pressure increase is noted. This occurs at a very shallow depth, usually less than feet, depending upon the formation, and indicates a resistance to flow up the outside of the pipes. When this occurs, normal circulation can be commenced, with the fluid being pumped at the rate of 100 to 125 gallons per minute for rapid, orderly retrieval of chips or cores.

If an increase in pump pressure is noted, indicating that the bit jets are clogged, the situation can be corrected promptly by stopping the bit penetration and by reversing the circulation to pump down the inner tube only.

Referring now to FIG. 6, the circulation method of this invention is illustrated in connection with apparatus for continuous coring. There, an annular coring bit 64 is carried at the lower end of the drill string 12 which, again, may be provided with an annular bridge or barrier 28 to protect the sub-surface formations from the circulating fluid. Also provided is a wedge or other suitable core breaker 66 which severs the cores C into suitable lengths to be carried to the surface by the fluid in the inner tube 16. Also, ports 60 may be provided to lighten the hydrostatic head and facilitate core retrieval.

Particularly when drilling in dry locations, it is desirable to have a small amount of fluid pass by the barrier 28 in order to provide some lubrication around the drill pipe 12 and to protect the bore hole wall W by building up a wall cake. Under certain circumstances it has been found desirable to provide a viscous, static lubricant fluid 68 in the hole annulus W and for this purpose I have found a gelatinous fluid containing polymers to be desirable. The viscous fluid is preferably introduced by closing the inner tube and pumping the drilling fluid slowly down the outer pipe annulus to circulate up the hole annulus until itreaches the surface. Then, drilling can be continued with a less viscous lighter drilling fluid. As long as the drilling fluid in the hole annulus is more viscous than the fluid being circulated, it will remain static and will restrict circulation of the fluid to the flow passages 18 and 20 within the drill pipe. If, however, the static fluid viscosity should become lessened as by dilution with surface water or the circulating fluid, the spotting procedure may be repeated.

While I have described by invention in conjunction with preferred embodiments thereof, it will become obvious that modifications and changes therein may be made by those skilled in the art without departing from the spirit and scope of my invention as defined by the claims appended hereto.

Having described my invention, I claim:

1. A method of drilling using a dual drill pipe string comprising attached sections of inner and outer pipes forming annular outer and circular inner flow passages, and a rotary drill bit comprising the steps of:

providing means around the drill pipe string at the lower end thereof to restrict fluid flow past it in a well annulus,

commencing a well bore by rotating the drill pipe string slowly while simultaneously introducing drilling fluid under pressure into both pipe flow passages at the upper ends thereof, and

when resistance to flow through both of said flow passages is increased, commencing further circulation of drilling fluid by introducing said drilling fluid under pressure in the outer pipe flow passage while exposing the inner passage to a relatively low pressure to permit the fluid to flow upward through the inner passage.

2. The method of drilling defined by claim 1 wherein:

the further circulation of drilling fluid is at a velocity in excess of 300 feet per minute.

3. The method of drilling defined by claim 2 wherein:

the drilling fluid is a liquid and is introduced into the outer passage at a rate in excess of 80 gallons a minute.

4. The method of drilling defined by claim 2 wherein:

the drilling fluid is a gas and is introduced into the outer passage at a rate in excess of 150 cubic feet per minute.

5. The method of drilling defined by claim 1 wherein the drilling fluid is a liquid and including the steps of:

providing at least one orifice in said drill string and drill bit assembly to bring said inner and outer passages into communication and introducing a compressed gas into said liquid.

6. The method of drilling defined by claim 1 including the step of at least partially evacuating the inner passage prior to commencing said further circulation.

7. The method of drilling defined by claim 6 wherein:

said inner passage is evacuated by pumping a compressed gas down it.

8. The method of drilling defined by claim 1 wherein:

in absence of said further circulation blocking off one of said pipe flow passages, and

pumping a viscous fluid slowly down the other pipe flow passage and enabling it to flow into the hole annulus.

9. The method of drilling a well bore using a dual concentric drill pipe string comprising attached sections of inner and outer pipes forming annular outer and circur lar inner flow passages, and a rotary drill bit, comprising the steps of:

providing at least one port through said inner pipe, rotating the drill pipe string while pumping a drilling liquid into said outer flow passage at the upper end thereof, and

introducing a compressed gas into said liquid at the upper end of said outer passage so that bubbles of said gas expand through said port.

10. The method defined by claim 9 including the step of:

providing means around the drill pipe string at the lower end thereof to restrict fluid flow past it in a well bore annulus.

References Cited UNITED STATES PATENTS 2,093,633 9/1937 Catland 175339 X 2,850,264 9/1958 Grable 17569 X 2,984,309 5/1961 Welchon 175-69 3,095,052 6/1963 Jackson 175-69 X 3,208,539 9/1965 Henderson 17569 X 3,292,719 12/1966 Schumacher 175-339 3,338,322 8/1967 Henderson 17569X NILE C. BYERS, JR., Primary Examiner.

US. Cl. X.R. 339 

